Flexible polymeric compositions have been prepared from sulfonated thermoplastic ionomers by incorporating a plasticizer in the ionomer (see U.S. Pat. No. 3,870,841). In order to incorporate the plasticizer into the polymeric ionomer, the polymer and plasticizer are dissolved in an organic solvent and the resulting solution is subsequently evaporated to dryness. This technique, however, is relatively expensive and inefficient and therefore has limited usefulness.
Polymeric compositions comprising emulsions of thermoplastic sulfonated polymers can be prepared, for example, by copolymerizing alkali metal salts of styrene sulfonic acid using a free radical initiator with a variety of thermoplastic forming monomers such as styrene, t-butyl styrene, chlorostyrene and the like. This technique leads to emulsions containing a high solids content which would be particularly useful in forming flexible films if it were possible to plasticize the solids in the emulsion. Attempts, however, to plasticize emulsions of thermoplastic sulfonated polymers have not been successful. Apparently, the viscosity and relatively high glass transition of the thermoplastic polymer as well as the water insolubility of the plasticizer prevent diffusion of the plasticizer into the emulsified polymer.
The present invention seeks to provide an efficient and practical method for plasticizing normally thermoplastic sulfonated polymeric ionomer emulsion.
It is an object of the present invention to provide a novel aqueous emulsion of a plasticized sulfonated thermoplastic polymer.
It is another object of the present invention to provide a method for preparing such a composition.
It is yet another object of the present invention to provide a composition suitable for forming films and flexible elastic coatings from a normally nonelastic thermoplastic sulfonated polymeric ionomers.